1. Field of the Invention
This invention relates to an injection device by which high-pressure fluid is injected into relatively inaccessible portions of various vessel nozzles provided on the side walls of a reactor pressure vessel (hereinbelow abbreviated as an RPV).
2. Discussion of Related Art
FIG. 1 shows the construction of a conventional boiling water reactor. In this figure, an RPV 1 accommodates coolant 2 and a core 3. The core 3 is accommodated in a shroud 4, and consists of a plurality of fuel assemblies and control rods (not shown).
The top of the shroud 4 is covered by a shroud head 5 above which are arranged steam separators 6 and steam dryer 7. The annular portion inside the RPV 1 and outside the shroud 4 is termed a downcomer 8.
The reactor output is controlled by using control rod drive mechanisms 9 to adjust the degree of insertion of the control rods into the reactor core 3.
Coolant 2 ascends through the core 3, where it is heated by the nuclear reaction taking place in the core 3. The heated coolant turns into a two-phase fluid consisting of water and steam, and this is fed into the steam separators 6.
The steam separated in the steam separators 6 is fed into the steam dryer 7, where it is dried to form dry steam. This dry steam is fed through main steam pipes 10 connected to the RPV 1 to a turbine system (not shown), to generate electricity. After performing work, the steam is fed to a condenser (not shown), where it is condensed to form condensate. This condensate is returned to the RPV 1 from a feed water nozzle 11, through a feed water system (not shown). Furthermore, the water separated by the steam separators 6 etc. flows down through downcomer 8 and is mixed with the feed water before being fed to the bottom of the core 3 by jet pumps 12.
A plurality of jet pumps 12 are arranged in the downcomer 8 and are equally spaced in the circumferential direction. A recirculation pump (not shown) is provided outside the RPV 1 and the recirculation system piping (not shown) is arranged between this recirculation pump and the jet pumps 12. The coolant is circulated in the core 3 by means of these jet pumps 12, the recirculation pump, and recirculation system piping (not shown). Reference numeral 13 in the drawings refers to recirculation inlet nozzles provided in the RPV 1. Riser pipes 14 of the jet pumps are connected on the inside of these recirculation inlet nozzles 13 through thermal sleeves 15 (FIG. 2). At the top end of the riser pipes 14 are connected branch pipes 16, from which the jet pump drive flow is supplied to the jet pumps 12.
The outer ends of the thermal sleeves 15 are welded to the inside faces of the recirculation inlet nozzles 13. Annular gaps 17 are formed between the outside faces of the thermal sleeves 15 and the inside faces of the recirculation inlet nozzles 13. Over many years of operation of the reactor, radioactive substances collect in these annular gaps 17. There is, therefore, concern that workers will be exposed to this accumulation of radioactive substances when non-destructive inspection is carried out from outside the RPV 1 during periodic inspection of the reactor.
It is therefore desirable to flush this radioactive substance from the gaps 17 prior to inspection. However, the recirculation inlet nozzles 13 are positioned at the lower part of the RPV 1. Because of this, when the reactor is shut down, the operation of washing away this accumulation by removing the RPV cap 18 and flushing with high-pressure water using a pipe lowered from the top of the RPV 1 is very difficult. In particular, this operation is made even more difficult by the fact that, as shown in FIG. 2, riser braces 19 for fixing the riser pipes 14 to the RPV 1 and the brackets 20 for mounting samples for examination of the effect produced by neutron irradiation of materials are mounted in the downcomer 8. Realization of a device to ensure a satisfactory flow of high pressure water for removal of this accumulation of radioactive substances is therefore required.
Coupling of recirculation inlet nozzles 13 and recirculation pipes 190 (shown by a chain-dotted line in FIG. 2) is performed by means of "safe-ends" 20a. Following prolonged operation, stress corrosion cracking may occur at the welds 21 of these safe-ends 20a and recirculation inlet nozzles 13. If such SCC should occur, in the known construction, replacement of safe-ends 20a is extremely difficult. Induction heating stress improvement (hereinbelow abbreviated as IHSI) is therefore carried out to convert the residual stresses in these welds 21 from tensile to compressive stresses. In such IHSI, a coil is wound round the outside of the welds and heating is performed by flowing high frequency electrical current through the coil while feeding cooling water into the annular gaps 17. This produces a temperature difference which gives rise to heat stress between the internal and external surfaces, the heat stress exceeding the yield point and thereby producing compressive residual heat stress at the internal surfaces in the neighborhood of the welds. Thus the introduction of high-pressure water to the inside of the nozzles 13 is required not only to remove the radioactive substances, as already mentioned, but also as cooling water during such induction heating.
The above description has been given with reference to the recirculation inlet nozzles, but the realization of an injection device as described above is also required for jet pump instrumentation nozzles 22 at the lower part of downcomer 8, as shown in FIG. 1.